Method and system for improving the performance of a fuel cell

ABSTRACT

An electrochemical fuel cell system adapted for maintaining the efficient production of electrical power. The system comprises a fuel supply containing a hydrogen rich gaseous fuel for delivery to a fuel cell. A fuel supply conduit connects the fuel supply and the fuel cell for delivering a fuel stream of the hydrogen rich gaseous fuel to the fuel cell. An impurity sensor is carried by the fuel supply conduit for detecting impurities in the fuel stream prior to the impurities entering the fuel cell. A heating mechanism is provided in communication with the impurity sensor being operatively associated with the fuel cell for changing the temperature of the fuel cell. The heating mechanism raises the temperature of the fuel cell from a normal operating temperature to an elevated operating temperature when the impurity sensor detects impurities in the fuel stream to prevent the impurities from interfering with fuel cell efficiency.

FIELD OF THE INVENTION

[0001] The present invention relates to a method and system forimproving the performance of electrochemical fuel cells, and moreparticularly, to a method and system for varying the temperature withinthe fuel cell to diminish electrocatalyst poisoning caused by impuritiesin the fuel stream.

[0002] Applicant claims priority of provisional application numbers60/362,615 and 60/363,077.

BACKGROUND OF THE INVENTION

[0003] As the power needs of society increase and with the depletion offossil fuels, there is a need for power services that provide cleanefficient power. Such needs exist both for mobile applications such asthe automotive industry and stationary applications as poweringmanufacturing facilities or commercial enterprises. To meet these needs,electrochemical fuel cells have been developed to convert the chemicalenergy of a fuel directly into electrical energy thereby providing aclean and efficient source of electrical power. Generally, a fuel cellincludes a pair of electrodes arranged across an electrolyte, whereinthe surface of one electrode is exposed to hydrogen or a hydrogen richgaseous fuel, and the surface of the other electrode is exposed to anoxygen-containing oxidizing gas, typically air. Inside the fuel cell,hydrogen rich gas from the fuel source reacts electrochemically at afirst electrode (anode) and is converted into protons and electrons by acatalyst. When converted, the protons move through an electrolyte to asecond electrode (cathode) that also includes a catalyst. The catalystinduces oxygen from an air supply to combine with the hydrogen protonsand electrons to form water, which is expelled from the fuel cell asvapor. The involvement of hydrogen and oxygen in the two reactions, onereleasing electrons and the other consuming them, yields electricalenergy across the anode and cathode by way of an external circuit,thereby generating electrical power.

[0004] Many electrochemical fuel cells employ a membrane electrodeassembly (“MEA”) in which the intermediate electrolyte comprises a solidpolymer electrolyte or ion-exchange membrane disposed between two porouselectrically conductive electrode layers (the anode and the cathode). Atthe anode, the fuel (H₂) is directed through a porous layer of the anodewhere it can be oxidized by the electrocatalyst to produce protons andelectrons from the hydrogen rich fuel. The protons migrate through thepolymer electrolyte membrane toward the cathode electrocatalyst to bindwith the oxygen and separated electrons from the hydrogen. Once acrossthe polymer electrolyte membrane, the oxidant (O₂) enters through theporous cathode to react with the protons and electrons on the cathodeelectrocatalyst to form water. The electrons travel from the anode tothe cathode through an external circuit, which produces an electricalcurrent.

[0005] The basic reaction for powering a hydrogen based fuel cell is asfollows:

Anode: 2H₂→4H⁺+4e⁻

Cathode: O₂+4H⁺+4e⁻→2H₂O

Overall: 2H₂+O₂→2H₂O

[0006] A process known as reforming produces hydrogen from hydrocarbonfuels such as methanol or gasoline. Unfortunately, the stream of fuelproduced by a reformer contains impurities that inhibit the desiredelectrochemical reaction within the fuel cell. These impurities areabsorbed chemically or physically on the surface of the anodeelectrocatalyst and prevent H₂ from bonding to active electrocatalystsites on the anode where it can be broken down into its protons andelectrons. By disrupting the anode reaction, the number of electronstraveling from anode to cathode is reduced and the efficiency of thefuel cell is detrimentally affected. Impurities in the fuel stream thatreduce the efficiency are known as electrocatalyst “poisons” and theireffect on fuel cells is known as “electrocatalyst poisoning.”Electrocatalyst poisoning results in reduced fuel cell performancethereby reducing the voltage output of the fuel cell for a given currentdensity.

[0007] Reformate fuel streams derived from hydrocarbons such as methanol(CH₃OH) contain high concentrations of H₂ and are well suited to fuelthe electrochemical fuel cell. However, such fuels also containelectrocatalyst poisons such as carbon monoxide (CO) that exist inrelatively small quantities in the fuel stream used to supply hydrogenrich gas to the fuel cell. The basic reactions for using methanol fuelto provide a hydrogen rich gas through a reformer for the fuel cell isshown as follows:

CH₃OH→2H₂+CO   (1)

CO+H₂O→H₂+CO₂   (2)

Overall: CH₃OH+H₂O→3H₂+CO₂

[0008] However, the above reactions do not practically result in theconversion of 100% of the carbon monoxide to CO₂ and causes thisimpurity to enter the fuel cell. In fact, most reformers typicallyproduce hydrogen gas containing up to 1% carbon monoxide. Additionalsteps can be taken to further reduce the carbon monoxide levels toaround 10-100 ppm, but under normal operation of the reformer, there aretransients that may cause the carbon monoxide levels to exceed the setpoints of normal operation for the reformer and the fuel cell. Evenminute amounts of carbon monoxide can cause substantial degradation ofthe fuel cell performance. To reduce the effects of poisoning on theanode electrocatalyst by impurities like carbon monoxide created by theincomplete reaction of trace amounts of carbon monoxide from the aboveequation, it is possible to pre-treat the fuel supply stream prior to itentering the fuel cell. However, these pretreatment methods for fuelstreams cannot effectively remove 100% of the carbon monoxide or otherimpurities that interfere with fuel cell efficiency. Even trace amountsof 10 ppm can result in electrocatalyst poisoning and cause asubstantial reduction in fuel cell performance. Increasing thetemperature of a fuel cell can reduce the ability of impurities to bondwith the electrocatalyst. However, maintaining the fuel cell at a highertemperature reduces the operational life of the fuel cell by damagingthe MEA and results in a reduction of the overall efficiency and usefullife of the fuel cell. It should be noted that while carbon monoxide isused in the above discussion, other impurities such as H₂S, NH₃, orother elements or compounds also degrade the performance of fuel cellsat both the anode and cathode sides of the cell. It is to be understoodthat impurities can also interfere with the cathode that can includeimpurities in the air added to the cathode. For example, hydrocarbonscan exist in the air in close proximity to a combustion engine or in theair as a hydrocarbon fuel station. Accordingly, the ability to reduceelectrocatalyst poisoning of a fuel cell at both the anode and cathodeis a problem to which significant attention should be directed.

[0009] Therefore, it is an object of the present invention to manipulatethe temperature of a fuel cell to reduce the ability of impurities inthe fuel cell fuel stream to bind with active electrocatalyst sites.

[0010] It is another object of the present invention to manipulate thetemperature of the fuel cell to reduce the effect of impurities whilereducing deterioration of the membrane electrode assembly.

SUMMARY OF THE INVENTION

[0011] The above objectives are accomplished according to the presentinvention by providing an electrochemical fuel cell system adapted formaintaining the efficient production of electrical power. The systemcomprising a fuel supply containing a hydrogen rich gaseous fuel fordelivery to a fuel cell. A fuel supply conduit connects the fuel supplyand the fuel cell for delivering a fuel stream of the hydrogen richgaseous fuel to the fuel cell. An impurity sensor is carried by the fuelsupply conduit for detecting impurities in the fuel stream prior to theimpurities entering the fuel cell. A heating mechanism is incommunication with the impurity sensor being operatively associated withthe fuel cell for changing the temperature of the fuel cell. The heatingmechanism raises the temperature of the fuel cell from a normaloperating temperature to an elevated operating temperature when theimpurity sensor detects impurities in the fuel stream. As a result, thedetrimental effect of impurities in the fuel stream on the normaloperation of the fuel cell is reduced.

[0012] In the preferred embodiment, the impurity sensor is constructedand arranged to detect a rise or drop in the level of impurities from apredetermine level of impurities. The impurity sensor signals theheating mechanism to raise the temperature of the fuel cell from thenormal operating temperature to the elevated operating temperature whenthe impurity sensor detects a rise in the level of impurities in thefuel stream above the predetermined level. The impurity sensor signalsthe heating mechanism to cease raising the temperature of the fuel celland return the fuel cell to the normal operating temperature when theimpurity sensor detects a drop in the level of impurities in the fuelstream below the predetermined level.

[0013] In a further advantageous embodiment, a control unit is providedin electronic communication with the impurity sensor and the heatingmechanism. The control unit monitors the level of impurities detected bythe impurity sensor and signals the heating mechanism to raise thetemperature of the fuel stream to raise the temperature of the fuel cellto the elevated operating temperature when a rise in the level ofimpurities is detected beyond a predetermined level. The control unitsignals the heating mechanism to cease raising the temperature of thefuel stream to return the fuel cell to the normal operating temperaturewhen the level of impurities monitored by the control unit and detectedby the impurity sensor drops below the predetermined level.

[0014] Preferably, the heating mechanism is activated to raise thetemperature of the fuel cell to the elevated operating temperature for apredetermined period of time upon detection of an impurity in the fuelstream. The heating mechanism is deactivated after the predeterminedperiod of time to return the fuel cell to the normal operatingtemperature so that after the impurity has pass completely through thefuel cell, the operating temperature can be decreased to preserveoperational life of the fuel cell.

[0015] In the preferred embodiment, the heating mechanism includes a hotgas injector connected to the fuel supply conduit. The hot gas injectorintroducing a stream of heated gas into the fuel supply conduit torapidly raise the temperature of the fuel cell so that the impuritiesare prevented from binding to electrocatalysts contained within the fuelcell. Preferably, the hot gas injector introduced heated hydrogen gasinto the fuel supply conduit to raise the temperature of the fuelstream.

[0016] In a further advantageous embodiment, the heating mechanismincludes a heating coil disposed around the fuel supply conduit. Theheating coil heats the fuel stream within the fuel supply conduit priorto entering the fuel cell to rapidly raise the temperature of the fuelcell so that the impurities are prevented from binding toelectrocatalysts contained within the fuel cell.

[0017] A voltage sensor may also be provided for detecting a rise ordrop in the voltage of the fuel cell from a predetermined voltage level.The voltage sensor is operatively associated with the heating mechanismfor signaling the heating mechanism to increase the temperature of thefuel cell to the elevated operating temperature when a drop in voltageis detected below the predetermined voltage level to remove impuritiesfrom the fuel cell. Additionally, the voltage sensor signals the heatingmechanism to cease raising the temperature of the fuel cell and returnthe fuel cell to the normal operating temperature when the voltagesensor detects a return in voltage to the predetermined voltage level.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The construction designed to carry out the invention willhereinafter be described, together with other features thereof. Theinvention will be more readily understood from a reading of thefollowing specification and by reference to the accompanying drawingsforming a part thereof, wherein an example of the invention is shown andwherein:

[0019]FIG. 1 is a schematic of the fuel cell system according to thepresent invention;

[0020]FIG. 2 is a schematic of the fuel cell system according to thepresent invention;

[0021]FIG. 3 is a graph showing the fuel cell voltage and affects ofconcentration of carbon monoxide according to temperature; and,

[0022]FIG. 4 is a flowchart depicting the change in temperatureaccording to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The present invention diminishes the effects of electrocatalystpoisoning by providing a method and system for varying the temperatureof the fuel cell according to the level of impurities present in thefuel stream. The temperature inside the fuel cell is rapidly changedfrom the normal operating temperature to a higher operating temperaturewhen a burst of carbon monoxide or other impurities are detected in thefuel stream. An impurity sensor is disposed along a fuel supply conduitto detect increased levels of impurities before the impurity can enterthe fuel cell. It is to be understood that various types of impuritysensors can be utilized to detect a variety of impurities in the fuelstream, such as CO, NH₃ and H₂S sensors. For illustrative purposed of apreferred embodiment, the impurity sensor is a carbon monoxide sensor.Additionally, the preferred embodiment is described for apolyelectrolyte membrane fuel cell (PEMFC) such as a membrane electrodeassembly (MEA) marketed under the trademark PRIMEA®. A temperaturechange of 70° C. to 90° C. for this fuel cell, occurring with the fuelcell maintained at a pressure of approximately 202 kPa, diminishes thepoisoning rate of impurities on the electrocatalyst. This temperaturechange is accomplished through the introduction of a burst of hot gasfrom a gas injector located downstream of the impurity sensor and beforethe fuel cell. In the preferred embodiment, the carbon monoxide sensorsends a signal to a control unit when a burst of carbon monoxide from areformer is detected. The control unit then signals the gas injector toopen a control valve and rapidly infuse heated H₂ into the fuel supplyconduit of the fuel cell, thereby raising the fuel cell temperature toprevent the binding of impurities on the electrocatalyst either bychemical or physical absorption to the electrocatalyst. In analternative embodiment, the existing fuel stream can be heated through aheating coil displaced around the injected fuel stream. Additionally, inthe event that some impurities do bind to the electrocatalyst, thehigher temperature increases the removal of the impurities from theelectrocatalyst, thereby increasing the voltage recover rate. Once theimpurity level returns to an acceptable concentration, reducing theoperating temperature from the raised temperature to the normaloperating temperature decreases the detrimental effect of theoperational life that higher temperatures cause. Therefore, once theimpurities sensor no longer detects elevated levels of impurities, orcarbon monoxide in this example, it sends a signal to the control unitwhich in turn signals the gas injector to close the control valve andcease the introduction of heated gas into the fuel supply conduit.

[0024] Referring now to the drawings, the invention will be described inmore detail. FIG. 1 shows a schematic of the fuel cell system accordingto the present invention. A reformer 14 receives methanol, hydrocarbonor other fuel from a fuel supply tank 10, along with water from a watersupply tank 12 for producing a hydrogen-rich gas that supplies the fuelcell. A fuel supply conduit 22 feeds a stream of hydrogen-rich gasproduced by the reformer to a fuel cell stack 28 at an anodeelectrocatalyst location, designated generally as 21. The constructionof fuel cells is well known by those skilled in the art and the presentinvention can be applied to any of the currently known fuel cellstructures and is not limited to any particular type of fuel cellarrangement. For alloy membranes normal operating temperature can begenerally 70° C. while the higher temperature can be generally 90° C.For ceramic membranes, normal operating temperatures can besignificantly higher and be in the several hundreds of degrees. Animpurity sensor 16 is disposed along fuel supply conduit 22 afterreformer 14 but before the gas enters fuel cell stack 28. By detectingthe impurity prior to the impurity reaching the fuel cell, the effect ofthe electrocatalyst poisoning can be minimized prior to experiencing thefull effect. It is to be understood that various types of impuritysensors can be utilized to detect a variety of impurities in the fuelstream, such as CO, NH3 and H₂S. For illustrative purposes of apreferred embodiment, the impurity sensor detects carbon monoxide. A gasinjector 18 for introducing heated gas into the system is connected tofuel supply conduit 22 after impurities sensor 16, but before fuelsupply conduit 22 enters fuel cell stack 28 at the anode. A controlvalve 19 for gas injector 18 is disposed along fuel supply conduit 22.Both impurities sensor 16 and gas injector 18 are in electroniccommunication with control unit 20. According to sensing a predeterminedlevel of poisoning such as a burst of carbon monoxide, impurities sensor16 sends a signal to control unit 20. Control unit 20 monitors thechanging level of impurities detected by sensor 16 and sends a signal togas injector 18 to open valve 19, thereby allowing heated gas to beinjected into fuel supply conduit 22 and thereby raising the fuel celltemperature to prevent the binding of impurities to the electrocatalysteither by chemical or physical absorption to the electrocatalyst.Additionally, for impurities that do bind to the electrocatalyst, thehigher temperature increases voltage recover rates and the rate ofimpurities are reduced within the fuel cell. Oxygen from air supply 26,is also included in the fuel supply delivered to the fuel cell stack.The oxygen is introduced into fuel cell stack 28 along cathode fuelconduit 24 at a cathode electrocatalyst location, designated generallyas 23, for completing the oxidation reaction that completes the fuelcell electrochemical oxidation/reduction reaction. In an alternativeembodiment, an additionally impurity sensor 16 can be placed in cathodefuel conduit 24 for detecting impurities in the oxygen supply to raisethe operating temperature of the fuel cell stack to prevent theimpurities from binding to the cathode.

[0025] In an alternative embodiment, a heating coil 30 (FIG. 2) can beused to heat the fuel stream prior to it entering the fuel cell. Theheating coil is connected to control unit 20 and heats the fuel streamupon impurities sensor 16 detecting a predetermined level of impurities.

[0026] Impurities sensor detects not only when the predetermined levelsof impurities exist, but also when the impurity level is reduced belowthe predetermined level so as to allow the operating temperature to bereduced. By reducing the operating temperature from the highertemperature to the normal operating temperature, the detrimental effecton the operational life of the fuel cell is reduced. Therefore, onceimpurity sensor 16 no longer detects elevated levels of carbon monoxide,it sends a signal to control unit 20 which in turn can signal gasinjector 18 to close control valve 19 and cease the introduction ofheated gas or cease heating the fuel stream being supplied to the fuelcell. This allows the fuel cell to return to the normal operatingconditions.

[0027] The controlled change of temperature extends the electrocatalystlife by only increasing operating temperature during high levels ofimpurities. As a result, an electrochemical fuel cell with increaseddurability and more uniform higher power output is provided.

[0028] Table 1 illustrates the advantages of increasing the temperatureof a fuel cell in response to increased levels of impurities. Thefollowing is provided for a polymer electrolyte membrane fuel cell(PEMFC) using a membrane electrode assembly (MEA) but this invention iscertainly not limited to this example. The following table showsdependence of poisoning and recovery rates on CO/H₂ mixture compositionat 600 mA/cm² with neat hydrogen as the baseline. Exposure to CO andbaseline level was 300 s and 1500 s respectively. T_(cell) = 70° C.,T_(cell) = 90° C., P = 202 kPa P = 202 kPa Poisoning Recovery PoisoningRecovery CO/H₂ rate rate rate rate (ppm) (V/min) (V/min) (V/min) (V/min)3000 −1.10 0.04 −0.08 0.06 10000 −1.56 0.03 −0.40 0.04

[0029] At a pressure of 202 kPa, by increasing the operating temperatureof the fuel cell from 70° C. to 90° C., in this example, the poisoningrate for carbon monoxide is decreased, though chemical and physicalcompeting absorption and oxidation through electrochemical or chemicalmeans. Additionally, the recovery rate of the fuel cell voltage is shownincreased by approximately 50%, thereby requiring less time for the fuelcell to regain its optimal operating efficiency. Thus, when a burst ofcarbon monoxide is detected by impurities sensor 16, the effect ofcarbon monoxide poisoning on the electrocatalyst can be mitigated byincreasing the operating temperature through the introduction of a burstof hot gas (dry or humid) into fuel supply conduit 22. As such, thecarbon monoxide poisoning rate, as noted in Table 1, is decreased due tothe increase in the fuel cell temperature. Thus, the fuel cell'sperformance is only minimally affected by the poisoning when the burstof hot gas is injected into the system before the impurity can enter thefuel cell. Since the higher temperature over time will reduce theoperational life of the fuel cell, it is beneficial to return the cellto the normal lower operating temperature as quickly as possible.Therefore, once impurities detector 16 no longer indicates unacceptablelevels of impurities, it signals control unit 20 to turn off gasinjector 18 to prevent further increase in temperature and allow fuelcell 28 to cool.

[0030] By monitoring impurity levels with control unit 20, prior to thefuel entering the fuel cell, it is possible to calculate the time thatthe carbon monoxide pulse will pass completely through the fuel cell.Thus, after the carbon monoxide pulse has passed, the hot gas injectorcan be controlled from control 20 allowing the system to decrease thefuel cell temperature to a normal operating temperature to preserve thefuel cell operational life. It is to be understood that this system andmethod can also be applied to a feedback scheme where impurities aredetected once they have entered the fuel cell and to mitigate theeffects of poisoning that has already entered the fuel cell.

[0031] In an alternative embodiment, a voltage sensor can be used tomeasure power output of the fuel cell in place of or in combination withthe impurities sensor. In this embodiment, the voltage sensor cantransmit a signal to the control unit for hot H₂ or actuating the heaterwhen the voltage level drops below a predetermined voltage level.Therefore, reacting to the resulting voltage drop by elevating thetemperature in the fuel cell can minimize the effect on voltage of anyimpurities entering the fuel cell. When the voltage stabilized, thecontrol unit can send a signal to the output control vales to stop theinjection of hot gas or deactivate the heater allowing the temperatureto return to normal so as to reduce the detrimental effect on the fuelcell and improve recovery rates. Additionally, a voltage sensor andimpurities sensor can operate in combination to detect impurities andvoltage drops so as to actuate the control unit to control temperatureproducing enhanced performance in the fuel cell. Software in the controlunit can detect the need to manipulating the temperature through theimpurities sensor or voltage sensor, send a control signal to the gasinjector or heater, detect the end of a burst of impurities or voltagedrop, and send a control signal to the injector or heater deactivatingthem.

[0032] Normal operation of the fuel cell at a normal operatingtemperature is preferred since it may be difficult to maintain optimumhumidity of the MEA at the higher temperatures. This is significantsince optimum humidity is required for optimum MEA and fuel cellperformance. Additionally, some fuel cells operate at lower temperatureconditions since external systems would be required to operate tomaintain higher temperature operating conditions requiring power. By wayof example, FIG. 3 illustrates the results of this invention for a MEAfuel cell during exposure to 3,000 ppm carbon monoxide for 5 seconds at600 MA/cm². Line 1 shows the transient in carbon monoxide concentrationsthat is detected by impurities sensor 16 (FIG. 1). Line 2 shows the fuelcell performance with a burst of carbon monoxide impurity, but withoutthis invention. In this instance the recover time for the cell voltageis substantially longer than with the use of this invention. Line 3shows the performance of the fuel cell when this invention increases infuel cell temperature upon detection of an impurity, carbon monoxideburst, and then a return to normal temperature after the impurity isflushed from the fuel cell. Without the use of this invention, a fuelcell operating at 600 MA/cm² shows a rapid decrease in cell voltage at70° C. when exposed to a large transient carbon monoxide impuritiesconcentration as shown in Line 2.

[0033] As shown in Line 3, the increase in temperature willsignificantly decrease the voltage drop to provide more uniform poweroutput. In an alternative embodiment, a heater is used for raising thetemperature of the injected gas and disengaged so the injected fuel isno longer to be heated so as to allow the fuel cell to return to normaloperating temperatures.

[0034] Referring now to FIG. 4, the method of operation of thisinvention is described in further detail. Additionally, the proceduraldescriptions are representations used by those skilled in the art tomost effectively convey the substance of this work to others skilled inthe art. These procedures are generally a self-contained sequence ofsteps leading to a desired result. In the event of the control unit,these steps require physical manipulations of physical quantities suchas electrical and magnetic signals capable of being stored, transferred,combined, compared, or otherwise manipulated. Therefore, this inventionis described with reference to flowchart illustrations of methods,apparatus, and computer program products according to the invention inorder to convey the understanding that each block of the flowchartillustration can be implemented by a set of computer readableinstructions embodied in a computer readable medium. These computerreadable instructions may be loaded onto a general purpose computer,special purpose computer, or other programmable data processingapparatus to produce the machine for which the instructions willexecute. It will be understood that each block of a flowchartillustration can be implemented by special purpose hardware basedcomputer systems that perform this specific function, or steps, incombination with special purpose hardware or computer instructions.

[0035] Referring now to FIG. 4, the fuel stream begins at step 32. Adetermination is made whether impurities exist in the fuel stream instep 34. If impurities do not exist, a determination is made on whetherthe temperature has previously been raised in step 40. If it has not,then the process returns to step 34. If in step 40, the temperature haspreviously been raised, then the temperature is lowered in step 42 andthe process returns to step 34. In step 34, if impurities do exist inthe stream, a determination can be made as to whether the impurities areabove a predetermined level in step 36. If they are not, then theprocess returns to step 34. In the event that the impurities are above apredetermined level, the determination is made as to whether thetemperature has previously been raised in step 38. If it has, then theprocess returns to step 34. In the event that the temperature has notbeen raised in step 38, then the temperature is raised in step 44, andthe process returns to step 34.

[0036] While a preferred embodiment of the invention has been describedusing specific terms, such description is for illustrative purposesonly, and it is to be understood that changes and variations may be madewithout departing from the spirit or scope of the following claims.

What is claimed is:
 1. An electrochemical fuel cell system adapted formaintaining the efficient production of electrical power of a fuel cell,said system comprising: a fuel supply containing a hydrogen rich fuelfor delivery to said fuel cell; a fuel supply conduit connecting saidfuel supply and said fuel cell for delivering a fuel stream of saidhydrogen rich fuel to said fuel cell; an impurity sensor carried by saidfuel supply conduit for detecting impurities in said fuel stream priorto said impurities entering said fuel cell; a heating mechanism incommunication with said impurity sensor being operatively associatedwith said fuel cell for changing the temperature of said fuel cell; and,said heating mechanism raising the temperature of the fuel cell from anormal operating temperature to an elevated operating temperature whensaid impurity sensor detects impurities in said fuel stream; whereby,the detrimental effect of impurities in the fuel stream on the normaloperation of the fuel cell is reduced.
 2. The system of claim 1 whereinsaid impurity sensor signals said heating mechanism to raise thetemperature of said fuel cell from said normal operating temperature tosaid elevated operating temperature when said impurity sensor detects arise in the level of impurities in said fuel stream above apredetermined level.
 3. The system of claim 2 wherein said impuritysensor signals said heating mechanism to cease raising the temperatureof said fuel cell and return the fuel cell to said normal operatingtemperature when said impurity sensor detects a drop in the level ofimpurities in said fuel stream below said predetermined level.
 4. Thesystem of claim 1 including a control unit in electronic communicationwith said impurity sensor and said heating mechanism.
 5. The system ofclaim 4 wherein said control unit signals said heating mechanism toraise the temperature of said fuel stream to raise the temperature ofsaid fuel cell to said elevated operating temperature when a rise in thelevel of impurities is detected above a predetermined level.
 6. Thesystem of claim 5 wherein said control unit signals said heatingmechanism to cease raising the temperature of said fuel stream to returnsaid fuel cell to said normal operating temperature when the level ofimpurities monitored by said control unit and detected by said impuritysensor drops below said predetermined level.
 7. The system of claim 1wherein said heating mechanism is activated to raise the temperature ofsaid fuel cell to said elevated operating temperature for apredetermined period of time upon detection of an impurity in said fuelstream; and said heating mechanism being deactivated after saidpredetermined period of time to return said fuel cell to said normaloperating temperature.
 8. The system of claim 1 wherein said heatingmechanism includes a hot gas injector connected to said fuel supplyconduit; said hot gas injector introducing a stream of heated gas intosaid fuel supply conduit to rapidly raise the temperature of said fuelcell so that said impurities are prevented from binding toelectrocatalysts contained within said fuel cell.
 9. The system of claim8 wherein said hot gas injector introduced heated hydrogen gas into saidfuel supply conduit to raise the temperature of said fuel stream. 10.The system of claim 1 wherein said heating mechanism includes a heatingcoil disposed around said fuel supply conduit; said heating coil heatingsaid fuel stream within said fuel supply conduit prior to entering saidfuel cell to rapidly raise the temperature of said fuel cell so thatsaid impurities are prevented from binding to electrocatalysts containedwithin said fuel cell.
 11. The system of claim 1 including a voltagesensor for detecting a rise or drop in the voltage of said fuel cellfrom a predetermined voltage level.
 12. The system of claim 11 whereinsaid voltage sensor is operatively associated with said heatingmechanism to increase the temperature of said fuel cell to said elevatedoperating temperature when a drop in voltage is detected below saidpredetermined voltage level to remove impurities from said fuel cell.13. The system of claim 12 wherein said voltage sensor is operativelyassociated with said heating mechanism to cease raising the temperatureof said fuel cell and return said fuel cell to said normal operatingtemperature when said voltage sensor detects a return in voltage to saidpredetermined voltage level.
 14. A system for maintaining the efficiencyof an electrochemical fuel cell of the type having a fuel supply fordelivering a hydrogen rich stream of fuel through a fuel supply conduitto a fuel cell stack, said system comprising: an impurity sensor fordetecting impurities in said fuel supply upstream of said fuel cellstack; a heating mechanism operatively associated with said fuel cellstack for changing the temperature of said fuel cell stack; and, acontrol unit operatively associated with said impurity sensor and saidheating mechanism for raising the temperature of said fuel cell stackwhen impurities are detected in said fuel supply; whereby, thedetrimental effect of impurities in the fuel stream on the normaloperation of the fuel cell is reduced.
 15. The system of claim 14wherein said control unit monitors the level of impurities detected bysaid impurity sensor and signals said heating mechanism to raise thetemperature of said fuel cell stack to an elevated operating temperaturewhen said control unit monitors a rise in the level of impurities abovea predetermined level.
 16. The system of claim 15 wherein said controlunit signals said heating mechanism to cease raising the temperature ofsaid fuel cell stack and return said fuel cell stack to a normaloperating temperature when said control unit monitors a drop in thelevel of impurities in said fuel supply to or below said predeterminedlevel.
 17. The system of claim 14 wherein said heating mechanism isactivated by said control unit to raise the temperature of said fuelcell stack to an elevated operating temperature for a predeterminedperiod of time upon detection of an impurity in said fuel stream; andsaid heating mechanism being deactivated by said control unit after saidpredetermined period of time to return said fuel cell stack to saidnormal operating temperature so that after said impurity has passcompletely through said fuel cell stack.
 18. The system of claim 14wherein said heating mechanism includes a hot gas injector connected tosaid fuel supply conduit; said hot gas injector introducing a stream ofheated gas into said fuel supply conduit to rapidly raise thetemperature of said fuel cell stack.
 19. The system of claim 14 whereinsaid heating mechanism includes a heating coil disposed around said fuelsupply conduit; said heating coil heating said stream of fuel withinsaid fuel supply conduit prior to entering said fuel cell stack torapidly raise the temperature of said fuel cell stack.
 20. The system ofclaim 14 including a voltage sensor for detecting a rise or drop in thevoltage of said fuel cell stack from a predetermined voltage level. 21.The system of claim 20 wherein said voltage sensor signals said heatingmechanism to increase the temperature of said fuel cell stack to anelevated operating temperature when a drop in voltage is detected belowsaid predetermined voltage level to remove impurities from said fuelcell stack.
 22. The system of claim 21 wherein said voltage sensorsignals said heating mechanism to cease raising the temperature of saidfuel cell and return said fuel cell to a normal operating temperaturewhen said voltage sensor detects a return in voltage to saidpredetermined voltage level.
 23. A method of improving the efficiency ofan electrochemical fuel cell system of the type having a fuel supply fordelivering a hydrogen rich stream of fuel through a fuel supply conduitto a fuel cell stack, said method comprising the steps of: detecting thepresence of impurities in said stream of fuel passing through said fuelsupply conduit; and, activating a heating mechanism to raise thetemperature of said fuel cell stack to an elevated operating temperatureupon detecting impurities in said stream of fuel.
 24. The method ofclaim 23 including the step of detecting a drop in the level ofimpurities below a predetermined level in said stream of fuel passingthrough said fuel supply conduit.
 25. The method of claim 24 includingthe step of deactivating said heating mechanism to lower the temperatureof said fuel cell stack to a normal operating temperature.
 26. Themethod of claim 23 including the step of heating said fuel cell stack byactivating a hot gas injector for rapidly infusing heated gas into saidfuel supply conduit.
 27. The method of claim 23 including the step ofheating said fuel cell stack by activating a heating coil disposedaround said fuel supply conduit for heating said stream of fuel prior toentering said fuel cell stack.
 28. The method of claim 23 including thestep of deactivating said heating mechanism after a predetermined periodof time expires and said impurities drop to a predetermine level. 29.The method of claim 23 including the step of detecting a drop in voltageof said fuel cell stack from a predetermined voltage level.
 30. Themethod of claim 29 including the step of activating said heatingmechanism to raise the temperature of said fuel cell stack to saidelevated operating temperature upon detecting a drop in voltage belowsaid predetermined voltage level.
 31. The method of claim 30 includingthe step of deactivating said heating mechanism to lower the temperatureof said fuel cell stack to a normal operating temperature when saidvoltage sensor detects a return in voltage to said predetermined voltagelevel.
 32. A method of improving the efficiency of an electrochemicalfuel cell system of the type having a fuel supply for delivering ahydrogen rich stream of fuel through a fuel supply conduit to a fuelcell stack, said method comprising the steps of: receiving a signalrepresenting the presence of impurities in said stream of fuel passingthrough said fuel supply conduit prior to said impurities entering saidfuel cell stack; and, sending a signal to a heating mechanism forraising the temperature of said stream of fuel to change the temperatureof said fuel cell stack from a normal operating temperature to anelevated operating temperature.
 33. The method of claim 32 including thestep of receiving a signal representing a decrease in the level ofimpurities in said stream of fuel.
 34. The method of claim 33 includingthe step of sending a signal to said heating mechanism to cease raisingthe temperature of said stream of fuel to return said fuel cell stack tosaid normal operating temperature.
 35. The method of claim 32 includingthe step of sending a signal to said heating mechanism to raise thetemperature of said fuel cell stack by activating a hot gas injector torapidly infusing heated gas into said fuel supply conduit.
 36. Themethod of claim 32 including the step of signaling said heatingmechanism to raise the temperature of said fuel cell stack by activatinga heating coil disposed around said fuel supply conduit for heating saidstream of fuel prior to entering said fuel cell stack.
 37. The method ofclaim 32 including the step of sending a signal to said heatingmechanism to deactivate after a predetermined period of time once saidimpurities drop below a predetermine level.
 38. The method of claim 32including the step of receiving a signal representing a drop in voltageof said fuel cell stack from a predetermined voltage level.
 39. Themethod of claim 38 including the step of sending a signal to saidheating mechanism to raise the temperature of said fuel cell stack tosaid elevated operating temperature upon a drop in voltage below saidpredetermined voltage level.
 40. The method of claim 39 including thestep of sending a signal to said heating mechanism to lower thetemperature of said fuel cell stack to said normal operating temperatureupon a return in voltage to said predetermined voltage level.